openvino/docs/OV_Runtime_UG/model_representation.md

Model Representation in OpenVINO™ Runtime

In OpenVINO™ Runtime a model is represented by the ov::Model class.

Model Representation

The ov::Model object stores shared pointers to ov::op::v0::Parameter, ov::op::v0::Result and ov::op::Sink operations that are inputs, outputs and sinks of the graph. Sinks of the graph have no consumers and are not included in the results vector. All other operations hold each other via shared pointers: child operation holds its parent (hard link). If an operation has no consumers and it's not the Result or Sink operation (shared pointer counter is zero), then it will be destructed and won't be accessible anymore.

Each operation in ov::Model has the std::shared_ptr<ov::Node> type.

For details on how to build a model in OpenVINO™ Runtime, see the [Build a Model in OpenVINO™ Runtime](@ref build_model) section.

Operations

The ov::Op class represents any abstract operation in the model representation. Use this class to create custom operations.

Operation Sets

Operation set (opset) is a collection of operations that can be used to construct a model. The ov::OpSet class provides a functionality to work with operation sets. For each operation set, OpenVINO™ Runtime provides a separate namespace, for example opset8. Each OpenVINO™ Release release introduces new operations and add these operations to a new operation set. New operation sets help to introduce a new version of operations that change behavior of previous operations. Using operation sets allows you to avoid changes in your application if new operations have been introduced.

Static and Partial Shapes

There are two types used for shape representation:

• ov::Shape - Represents static (fully defined) shapes.

• ov::PartialShape - Represents dynamic shapes. That means that the rank or some of dimensions are dynamic (undefined). ov::PartialShape can be converted to ov::Shape using the get_shape() method if all dimensions are static; otherwise the conversion raises an exception.

Build a Model in OpenVINO™ Runtime

You can create a model from source. This section illustrates how to construct a model composed of operations from an available operation set.

Operation set opsetX integrates a list of pre-compiled operations that work for this purpose. In other words, opsetX defines a set of operations for building a graph.

For a complete list of operation sets supported in OpenVINO™ toolkit, see Available Operations Sets.

To add suport of custom operations, see the Add Custom OpenVINO Operations document.

To build an ov::Model instance from opset8 operations, include the following files:

• C++ @snippet example_ngraph_utils.cpp ov:include

• Python

   import openvino.runtime.opset8 as ov
   from openvino.runtime import Model
  

The following code demonstrates how to create a simple model:

• C++ @snippet example_ngraph_utils.cpp ov:create_simple_model

• Python

  TBD
  

The following code creates a model with several outputs:

• C++ @snippet example_ngraph_utils.cpp ov:create_advanced_model

• Python

  TBD
  

FAQ

Does OpenVINO™ Runtime provide any capabilities to debug the model structure and model modification?

• To receive additional messages about applied graph modifications, rebuild the OpenVINO™ Runtime library with the -DENABLE_OPENVINO_DEBUG=ON option.
• A model can be visualized to image from the xDot format: @snippet example_ngraph_utils.cpp ov:visualize
• A model can be serialized to IR: @snippet example_ngraph_utils.cpp ov:serialize

How can I develop my own transformation pass?

See the Transformations Developer Guide.

See Also

• Available Operation Sets
• OpenVINO™ Runtime Extensibility Developer Guide